Polishing apparatus and method of manufacturing semiconductor device using the same

ABSTRACT

A polishing apparatus includes: a wafer polishing unit including a polishing surface plate, an abrasive supply part supplying an abrasive to a polishing pad placed on the polishing surface plate, and a wafer holding part holding a semiconductor wafer; and a dressing unit including a dresser. The dresser has a pellet-shaped grindstone with abrasive particles fixed to a surface thereof. The pellet-shaped grindstone is divided into a first region along an outer peripheral portion thereof and a second region located inside the first region. A chipping preventing portion for the abrasive particles is provided in the first region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2009-063965, filed on Mar. 17, 2009; the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a polishing apparatus and a method of manufacturing a semiconductor device using the same.

2. Description of the Related Art

In the manufacturing process of a semiconductor device, for example, a chemical mechanical polishing (CMP) method is often used when planarizing the surface of a semiconductor wafer in the process of forming multilevel metallization or the isolation process. The planarizing process (polishing process) of the semiconductor wafer to which the CMP method is applied is implemented by pressing the surface to be polished of the semiconductor wafer against a polishing pad while supplying an abrasive in a slurry form onto the polishing pad. The polishing pad degrades in polishing performance due to occurrence of clogging in the surface or flattening of the surface caused by repeatedly performed polishing process on the semiconductor wafers. For this reason, the dressing of the surface of the polishing pad is implemented after the polishing of the semiconductor wafer, at the start up and so on.

To the dressing of the polishing pad, a dresser using diamond abrasive particles or the like is applied. For example, in the pellet-type dresser in which a plurality of pellet-shaped grindstones are bonded to a baseplate, a pellet-shaped grindstone in which diamond abrasive particles are formed in a pellet shape using a resin, or a pellet-shaped grindstone in which diamond abrasive particles are fixed to a metal base in the shape corresponding to the pellet, is used.

The pellet-type dresser has gaps among the pellet-shaped grindstones, and therefore has an advantage of being superior in discharging property of the abrasive and the polished waste. The dresser having pellet-shaped grindstones with the diamond abrasive particles fixed to the metal bases, however, has a disadvantage of being susceptible to chipping of the diamond abrasive particles at the dressing of the polishing pad due to an impact. Especially when the polishing pad is hard or when the shape of the grooves of the polishing pad tends to affect the diamond abrasive particles, the diamond abrasive particles are susceptible to chipping. If the chipped diamond abrasive particles are mixed into the abrasive for the semiconductor wafer, scratch may be caused or crack of a wafer may occur, at the polishing of the semiconductor wafer.

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the present invention there is provided a polishing apparatus including: a wafer polishing unit including a polishing surface plate, an abrasive supply part supplying an abrasive to a polishing pad placed on the polishing surface plate, and a wafer holding part holding a semiconductor wafer, the wafer polishing unit polishing a surface to be polished of the semiconductor wafer held on the wafer holding part by pressing the surface to be polished of the semiconductor wafer against the polishing pad; and a dressing unit including a dresser having a pellet-shaped grindstone with abrasive particles fixed to a surface thereof, the dressing unit dressing a surface of the polishing pad using the pellet-shaped grindstone, wherein the pellet-shaped grindstone has a first region along an outer peripheral portion thereof and a second region located inside the first region, and comprises a chipping preventing portion for the abrasive particles provided in the first region.

According to another aspect of the present invention there is provided a method of manufacturing a semiconductor device using the polishing apparatus according to the above aspect of the present invention, the method including: polishing the surface to be polished of the semiconductor wafer held on the wafer holding part by pressing the surface to be polished of the semiconductor wafer against the polishing pad; and dressing the surface of the polishing pad using the pellet-shaped grindstone before, after, or during the polishing of the semiconductor wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a polishing apparatus according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a dresser used in the polishing apparatus shown in FIG. 1.

FIGS. 3A to 3C are views each showing the structure of a pellet-shaped grindstone used in the dresser shown in FIG. 2, FIG. 3A being a sectional view showing a first embodiment, FIG. 3B being a sectional view showing a second embodiment, and FIG. 3C being a sectional view showing a third embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments for implementing the present invention will be described. FIG. 1 is a perspective view schematically showing a structure of a polishing apparatus according to an embodiment of the present invention. The polishing apparatus 1 is mainly composed of a wafer polishing unit including a polishing surface plate 3, an abrasive supply part 4, and a wafer holding part 6 holding a semiconductor wafer 5; and a dressing unit including a dresser 7. Further, a method of manufacturing a semiconductor device according to an embodiment of the present invention includes a step of polishing a surface to be polished of the semiconductor wafer 5 using the polishing apparatus 1, and a step of dressing the surface of a polishing pad 2 placed on the polishing surface plate 3 using the dresser 7 before, after, or during the polishing of the semiconductor wafer 5.

In the polishing apparatus 1 shown in FIG. 1, a rotation shaft 8 is provided on a lower surface side of the polishing surface plate 3. The rotation shaft 8 is connected to a rotation drive mechanism whose illustration is omitted. The polishing surface plate 3 is rotatable in an X-direction with an arrow in FIG. 1 around the rotation shaft 8. The polishing pad 2 is bonded on the surface of the polishing surface plate 3. The polishing pad 2 may be any of a soft pad and a hard pad. To the polishing pad 2 located on the polishing surface plate 3, an abrasive in a slurry form is supplied from the abrasive supply part 4. The abrasive is arbitrarily selected according to the polishing condition. The metal oxide particles such as cerium oxide particles, alumina particles or silica particles dispersed in water, an organic solvent or the like into a slurry form may be used as the abrasive.

The wafer holding part 6 has a rotation head 9 in a disk form. On the surface of the rotation head 9 opposed to the polishing pad 2, a wafer holding mechanism 10 is provided which holds, for example, by suction the semiconductor wafer 5 being the article to be polished. The semiconductor wafer 5 held by the wafer holding part 6 is placed such that its surface to be polished comes into contact with the polishing pad 2. The wafer holding part 6 presses the surface to be polished of the semiconductor wafer 5 against the polishing pad 2 at a predetermined pressure while rotating the semiconductor wafer 5 in a Y-direction with an arrow in FIG. 1.

The polishing apparatus 1 of the embodiment presses the surface to be polished of the semiconductor wafer 5 against the polishing pad 2 at the predetermined pressure while supplying the abrasive in a slurry form onto the polishing pad 2 from the abrasive supply part 4, to thereby perform chemical mechanical polishing (CMP) on the surface to be polished of the semiconductor wafer 5 into a desired state based on the rotation of the semiconductor wafer 5 itself and the rotation of the polishing surface plate 3 having the polishing pad 2. The polishing apparatus 1 of the embodiment may be used as a CMP apparatus.

When the polishing step (CMP step) for the semiconductor wafer 5 is implemented using the polishing apparatus 1 shown in FIG. 1, the polishing performance of the polishing pad 2 deteriorates because its surface is clogged with the abrasive particles, polished waste and so on or its surface is flattened. For this reason, the polishing apparatus 1 includes the dresser 7 which dresses the surface of the polishing pad 2. The dresser 7 is rotatably attached to the tip of a turnable arm 11. The dressing of the polishing pad 2 after the polishing of the semiconductor wafer 5 or at start-up of the apparatus is performed by bringing the dresser 7 into contact with the entire surface of the polishing pad 2 while pressing the dresser 7 at the predetermined pressure against the polishing pad 2 and swinging or rotating the dresser 7 as necessary.

The dressing of the polishing pad 2 includes a dressing of the polishing pad 2 at start-up of the polishing apparatus 1, a dressing of the polishing pad 2, or a removal treatment of a degraded layer and the polished waste during and after the polishing of the semiconductor wafer 5, and so on. The dresser 7 implementing the dressing includes a plurality of pellet-shaped grindstones 13 attached to the surface of a baseplate 12 in a disk shape (a surface opposed to the polishing pad 2) as shown in FIG. 2. The pellet-shaped grindstone 13 has an abrasive particle layer 15 fixed to the surface of a metal base 14 in a disk shape corresponding to the pellet shape. In the dresser 7 including the plural pellet-shaped grindstones 13, each abrasive particle layer 15 is arranged to face the polishing pad 2.

The abrasive particle layer 15 of the pellet-shaped grindstone 13 is typically composed of diamond abrasive particles. The diamond abrasive particles may be of any of the irregular type or the blocky type. The diamond abrasive particles of the irregular type are superior in the dressing effect (the conditioning characteristic of the polishing pad 2) but susceptive to chipping due to an impact at the dressing. Therefore, the dresser 7 in the embodiment is suitable for the case using the pellet-shaped grindstones 13 having the abrasive particle layers 15 composed of the diamond abrasive particles of the irregular type. Note that BN abrasive particles (CBN abrasive particles) or the like may also be used in place of the diamond abrasive particles.

The abrasive particle layer 15 is made by fixing the diamond abrasive particles or the like to the surface of the metal base 14. The methods of fixing the diamond abrasive particles to the metal base 14 include common electrodeposition method, metal bonding method, resin bonding method, brazing method and so on. The particle size and the arrangement density and so on of the abrasive particles constituting the abrasive particle layer 15 are arbitrarily set according to the dressing conditions. The dressing of the surface of the polishing pad 2 is implemented by relatively moving the dresser 7 to the polishing pad 2 while pressing the abrasive particle layers 15 against the surface of the polishing pad 2 at the predetermined pressure.

The polishing apparatus 1 includes the pellet-type dresser 7. The dresser 7 has gaps among the pellet-shaped grindstones 13, and therefore has an advantage of being superior in discharging property of the abrasive and the polished waste and so on but has a disadvantage of being susceptible to chipping of abrasive particles at the dressing of the polishing pad 2. The dresser 7 has a larger edge amount because an edge portion (an end face) exists at each abrasive particle layer 15 of the pellet-shaped grindstones 13. In the case where the dressing is performed by pressing the abrasive particle layers 15 against the polishing pad 2, an impact is applied on the edge portions of the abrasive particle layers 15, so that the abrasive particles constituting the abrasive particle layers 15 are more susceptible to chipping as the edge amount is larger.

Hence, a chipping preventing portion for abrasive particles is provided in an outer peripheral region (a region including the edge portion (the end face)) of each abrasive particle layer 15 of the pellet-shaped grindstones 13 in the polishing apparatus 1 of the embodiment. The concrete structures of the pellet-shaped grindstone 13 of the embodiment will be described with reference to FIGS. 3A to 3C. FIG. 3A is a sectional view showing the structure of a pellet-shaped grindstone 13A according to a first embodiment. FIG. 3B is a sectional view showing the structure of a pellet-shaped grindstone 13B according to a second embodiment. FIG. 3C is a sectional view showing the structure of a pellet-shaped grindstone 13C according to a third embodiment.

The abrasive particle layer 15 of each of the grindstones 13A, 13B and 13C according to the first to third embodiments is composed of abrasive particles (e.g. diamond abrasive particles) 17 fixed to the surface of the metal base 14 via a fixing layer 16. As described above, an electrodeposition layer, a metal bonding layer, a resin bonding layer or the like is employed as the fixing layer 16. Such an abrasive particle layer 15 is divided into a first region A1 along its outer peripheral portion (an edge portion) and a second region A2 located inside the first region A1. Each of the pellet-shaped grindstones 13A, 13B and 13C of the respective embodiments has the first region A1, that is, a chipping preventing portion 18 for the abrasive particles 17, provided in the outer peripheral region including the edge portion.

The pellet-shaped grindstone 13A according to the first embodiment has a resin coating 19 covering the abrasive particles 17 existing in the first region A1 as the chipping preventing portion 18 as shown in FIG. 3A. In other words, the abrasive particles 17 in the first region A1 susceptible to chipping at the dressing are covered by the resin coating 19 and the edge portion (the end face) of the abrasive particle layer 15 is composed of a resin material, thereby making it possible to suppress the chipping of the abrasive particles 17 due to an impact on the edge portion (the end face).

The resin coating 19 can be formed by applying any known coating techniques. As the resin coating 19, a resin material is used which is highly wettable to the metal base 14, the fixing layer 16 and so on and thus excellent in adhesiveness. Examples of concrete material constituting the resin coating 19 include an acrylic resin, a fluorine based resin and so on. If the wettability is insufficient, an intermediate layer may be provided between the metal base 14 and the resin coating 19. Note that the resin coating 19 may be formed to cover also the end face (an outer peripheral side surface) of the metal base 14.

The first region A1 forming the resin coating 19 as the chipping preventing portion 18 for the abrasive particles 17 is preferably set such that its width from the outer edge of the pellet-shaped grindstone 13A falls within a range not less than 1% nor more than 10% of the outer diameter of the pellet-shaped grindstone 13A. If the width of the first region A1 is less than 1% of the outer diameter of the pellet-shaped grindstone 13A, the first region A1 may not sufficiently attain the chipping preventing effect for the abrasive particles 17. On the other hand, if the width of the first region A1 exceeds 10% of the outer diameter of the pellet-shaped grindstone 13A, the area of the second region A2 taking charge of the dressing operation relatively decreases, so that the conditioning characteristics of the polishing pad 2 may be deteriorated.

Though the concrete width of the first region A1 depends on the outer diameter of the pellet-shaped grindstone 13A, it is preferable to set the first region A1 in a range not less than 0.1 mm nor more than 3 mm from the outer peripheral portion of the pellet-shaped grindstone 13A, for example, for the pellet-shaped grindstone 13A having an outer diameter of about 10 mm to 30 mm. It is preferable to similarly set the width of the first region A1 also for the pellet-shaped grindstone 13B of the second embodiment and the pellet-shaped grindstone 13C of the third embodiment which will be described later in detail.

Preferably, the thickness of the resin coating 19 is half or less of the projecting amount of the abrasive particles 17 and in the range with which the resin coating 19 can be stably formed as a film. As used herein, the “projecting amount of the abrasive particles 17” means a value determined, for example, by subtracting the thickness of the fixing layer 16 from the average particle size of the abrasive particles 17. If the thickness of the resin coating 19 exceeds the half of the projecting amount of the abrasive particles 17, the dressing effect of the polishing pad 2 by the pellet-shaped grindstones 13A may decrease. For example, if the diamond abrasive particles 17 having an average particle size of 150 μm are fixed using a Ni electrodeposition layer (the fixing layer 16) having a thickness of about 100 μm, the projecting amount of the diamond abrasive particles 17 is about 50 μm. In such a case, for example, the coating 19 made of an acrylic resin may be formed to have a thickness of about 20 μm on the first region A1.

With the pellet-shaped grindstone 13A according to the first embodiment, since the abrasive particles 17 in the first region A1 are covered by the resin coating 19, the chipping of the abrasive particles 17 due to the impact on the edge portion (the end face) at the dressing of the polishing pad 2 can be suppressed. Specifically, even in the case using the hard polishing pad 2 or the case where the groove shape of the polishing pad 2 tends to affect the abrasive particles 17, the chipping of the abrasive particles 17 can be stably suppressed. Accordingly, it becomes possible to suppress scratch or crack of a wafer that is a problem at the polishing of the semiconductor wafer 5 caused by mixing of the chipped abrasive particles 17 into the abrasive in a slurry form. In other words, the polishing accuracy and the polishing efficiency of the semiconductor wafer 5 can be enhanced.

The pellet-shaped grindstone 13B according to the second embodiment has a ceramic coating 20 covering the abrasive particles 17 existing in the first region A1 as the chipping preventing portion 18 as shown in FIG. 3B. In other words, the abrasive particles 17 in the first region A1 susceptible to chipping at the dressing are covered by the ceramic coating 20 and the edge portion (the end face) of the abrasive particle layer 15 is composed of a ceramic material, thereby making it possible to suppress the chipping of the abrasive particles 17 due to an impact on the edge portion (the end face) at the dressing of the polishing pad 2.

The ceramic coating 20 can be formed by applying any known coating techniques. As the ceramic coating 20, a ceramic material may be used which is hard and excellent in adhesiveness to the metal base 14 and so on. Examples of concrete material constituting the ceramic coating 20 include amorphous silicon carbide. The ceramic coating 20 may be formed to cover also the end face (an outer peripheral side surface) of the metal base 14.

Preferably, the thickness of the ceramic coating 20 is half or less of the projecting amount of the abrasive particles 17 and in the range with which the ceramic coating 20 can be stably formed as a film. If the thickness of the ceramic coating 20 exceeds the half of the projecting amount of the abrasive particles 17, the dressing effect may decrease. For example, if the diamond abrasive particles 17 having an average particle size of 150 μm are fixed using a Ni electrodeposition layer (the fixing layer 16) having a thickness of about 100 μM, the projecting amount of the diamond abrasive particles 17 is about 50 μm. In such a case, for example, the coating 20 made of amorphous silicon carbide may be formed to have a thickness of about 5 μm on the first region A1.

With the pellet-shaped grindstone 13B according to the second embodiment, since the abrasive particles 17 in the first region A1 are covered by the ceramic coating 20, the chipping of the abrasive particles 17 due to the impact on the edge portion (the end face) at the dressing can be suppressed. Specifically, even in the case using the hard polishing pad 2 or the case where the groove shape of the polishing pad 2 tends to affect the abrasive particles 17, the chipping of the abrasive particles 17 can be stably suppressed. Accordingly, it becomes possible to suppress scratch or crack of a wafer that is a problem at the polishing of the semiconductor wafer 5 caused by mixing of the chipped abrasive particles 17 into the abrasive. In other words, the polishing accuracy and the polishing efficiency of the semiconductor wafer 5 can be enhanced.

The pellet-shaped grindstone 13C according to the third embodiment has a guide member 21 provided in the first region A1 as the chipping preventing portion 18 as shown in FIG. 3C. In the pellet-shaped grindstone 13C, the abrasive particles 17 are arranged only in the second region A2. Accordingly, the guide member 21 is provided to cover the first region A1 where no abrasive particles 17 are fixed. The guide member 21 has, for example, a ring shape corresponding to the first region A1. Note that the guide member 21 may have a shape to cover also the end face (an outer peripheral side surface) of the metal base 14.

The guide member 21 may be composed of a resin material or a ceramic material. Concrete examples of the resin material include a fluorine based resin and so on excellent in abrasion resistance, lubrication property and so on. Concrete examples of the ceramic material include silicon nitride, silicon carbide and so on excellent in abrasion resistance. In the case where the guide member 21 is composed of the ceramic material, it is preferable to make the surface roughness thereof (the roughness of the surface facing the polishing pad 2) low in order to improve the lubrication property and so on. The guide member 21 may be made by attaching a member in a desired shape (for example, a ring member) to the first region A1 or formed by the coating method as in the first and second embodiments.

The top of the guide member 21 is preferably located at a position lower by 20 μm or more than the highest position of the projecting height of the abrasive particles 17. If the height of the guide member 21 is higher than the position, the dressing effect by the abrasive particle layer 15 may decrease. For example, it is assumed that the diamond abrasive particles 17 having an average particle size of 100 μm are fixed only to the second region A2 and the height of the diamond abrasive particle 17 having the largest projecting height among them is 120 μm. In such a case, the guide member 21 having a height of 100 μm may be attached, for example, to the first region A1.

As described above, no abrasive particles 17 are fixed to the first region A1 where the chipping tends to occur at the dressing, and the guide member 21 is disposed in the first region A1 so that the edge portion (the end face) of the abrasive particle layer 15 is composed of the resin material or the ceramic material, thereby making it possible to suppress the chipping of the abrasive particles 17 due to an impact on the edge portion (the end face) at the dressing. Specifically, even in the case using the hard polishing pad 2 or the case where the groove shape of the polishing pad 2 tends to affect the abrasive particles 17, the chipping of the abrasive particles 17 can be stably suppressed. Accordingly, it becomes possible to suppress scratch or crack of a wafer that is a problem at the polishing of the semiconductor wafer 5 caused by mixing of the chipped abrasive particles 17 into the abrasive. In other words, the polishing accuracy and the polishing efficiency of the semiconductor wafer 5 can be enhanced.

When dressing of the hard polishing pad (NCP-1 manufactured by Japan Micro Coating Co., Ltd.) 2 was implemented using the dresser 7 to which 36 pellet-shaped grindstones 13A according to the first embodiment were attached, it was confirmed that no chipping occurred in the diamond abrasive particles 17. To verify this point, when the polishing of a dummy semiconductor wafer 5 was implemented using the polishing pad 2 treated by the dresser 7, it was confirmed that diamond scratch due to the chipping of the diamond abrasive particles 17 did not occur. Note that the polishing conditions were set such that the load was 40 kPa, the number of rotations of the polishing surface plate 3 was 100 rpm, the number of rotations of the rotation head 9 was 107 rpm, and the polishing time was 60 seconds. As the abrasive, a cerium oxide slurry (to which polyacrylic acid was added by 3 mass % as a surfactant) was used.

On the other hand, when dressing of the same polishing pad (NCP-1 manufactured by Japan Micro Coating Co., Ltd.) was implemented using the dresser to which 36 pellet-shaped grindstones (pellet-shaped grindstones made by only fixing diamond abrasive particles to the entire surface of the metal base) having no chipping preventing portion for the abrasive particles, chipping was found in the diamond abrasive particles at the outer peripheral portion. When the polishing of a dummy semiconductor wafer was implemented using the polishing pad treated by such a dresser, a large scratch caused by the chipping of the diamond abrasive grain was confirmed. Note that also in the cases using the pellet-shaped grindstones 13B and 13C according to the second and third embodiments, it was confirmed that the same result as that by the pellet-shaped grindstone 13A according to the first embodiment was obtained.

Further, in order to evaluate the polishing performance of the polishing pad (NCP-1 manufactured by Japan Micro Coating Co., Ltd.) 2 treated by the dresser 7 to which 36 pellet-shaped grindstones 13A according to the first embodiment were attached, polishing of a semiconductor wafer having a silicon oxide film (a blanket film) was implemented. The polishing conditions were set such that the load was 15 kPa, the number of rotations of the polishing surface plate 3 was 100 rpm, the number of rotations of the rotation head 9 was 107 rpm, and the polishing time was 50 seconds. As the abrasive, a cerium oxide slurry (to which polyacrylic acid was added by 3 mass % as a surfactant) was used. The dressing of the polishing pad 2 by the dresser 7 was implemented immediately after every wafer polishing. The dressing conditions were set such that the load was 200 N and the treatment time was 30 seconds.

The polishing was implemented on semiconductor wafers in succession, semiconductor wafers were extracted one each after polishing of one semiconductor wafer, polishing of 24 semiconductor wafers, polishing of 48 semiconductor wafers, and polishing of 72 semiconductor wafers, and the polishing rates thereof were investigated. As a result of this, the polishing rate of about 450 nm/min was achieved in each of them. This is the value equal to that in the case of treatment by the dresser using the pellet-shaped grindstones having no chipping preventing portions for abrasive particles, from which it was confirmed that the excellent and stable polishing rate could be achieved. Note that also in the cases using the pellet-shaped grindstones 13B and 13C according to the second and third embodiments, it was confirmed that the same result as that by the pellet-shaped grindstone 13A according to the first embodiment could be obtained.

Next, planarization by CMP was implemented on the semiconductor wafer having a pattern formed thereon. The pattern was formed as follows. First, steps having a height of 600 nm were formed on a silicon substrate by common lithography method and dry-etching method, and the dimensions of the line and space of the steps were changed to form the pattern having a region with a high convex coverage (90%) and a region with a low convex coverage (10%). The area of each of the regions was 4×4 mm. On such a silicon substrate, a silicon oxide film (SiO₂ film) was formed to have a thickness of 110 nm by the CVD method. The silicon oxide film is formed with concave and convex parts.

Polishing was implemented on the semiconductor wafer having such a concave/convex pattern. The polishing conditions were set such that the load was 30 kPa, the number of rotations of the polishing surface plate 3 was 100 rpm, the number of rotations of the rotation head 9 was 107 rpm, and the polishing time was 60 seconds. As the abrasive, a cerium oxide slurry (to which polyacrylic acid was added by 3 mass % as a surfactant) was used. This was supplied onto the polishing pad 2 at a flow rate of 190 cc/min. The dressing of the polishing pad 2 by the dresser 7 was implemented immediately after every wafer polishing. The dressing conditions were set such that the load was 200 N and the treatment time was 30 seconds.

The polishing was implemented on semiconductor wafers in succession, semiconductor wafers were extracted one each after polishing of one semiconductor wafer, polishing of 24 semiconductor wafers, polishing of 48 semiconductor wafers, and polishing of 72 semiconductor wafers, and the global step height thereof were investigated. As a result of this, the global step height of each of them was within 110 to 130 nm. This is the value equal to that in the case of treatment by the dresser using the pellet-shaped grindstones having no chipping preventing portions for abrasive particles, from which it was confirmed that the global step height was also stable. Note that also in the cases using the pellet-shaped grindstones 13B and 13C according to the second and third embodiments, it was confirmed that the same result as that by the pellet-shaped grindstone 13A according to the first embodiment could be attained.

Note that the present invention is not limited to the above-described embodiments, but is applicable to a polishing apparatus using a dresser with pellet-shaped grindstones and all methods of manufacturing a semiconductor device including a step of polishing a semiconductor wafer by the polishing apparatus. Such polishing apparatus and methods of manufacturing the semiconductor device are also included in the present invention. Further, the embodiments of the present invention can be extended or changed, and the extended and changed embodiments are also included in the technical scope of the present invention. 

1. A polishing apparatus, comprising: a wafer polishing unit comprising a polishing surface plate, an abrasive supply part supplying an abrasive to a polishing pad placed on the polishing surface plate, and a wafer holding part holding a semiconductor wafer, the wafer polishing unit polishing a surface to be polished of the semiconductor wafer held on the wafer holding part by pressing the surface to be polished of the semiconductor wafer against the polishing pad; and a dressing unit comprising a dresser having a pellet-shaped grindstone with abrasive particles fixed to a surface thereof, the dressing unit dressing a surface of the polishing pad using the pellet-shaped grindstone, wherein the pellet-shaped grindstone has a first region along an outer peripheral portion thereof and a second region located inside the first region, and comprises a chipping preventing portion for the abrasive particles provided in the first region.
 2. The polishing apparatus as set forth in claim 1, wherein the chipping preventing portion for the abrasive particles comprises a resin coating covering the abrasive particles fixed to the first region.
 3. The polishing apparatus as set forth in claim 2, wherein the resin coating is formed of an acrylic resin or a fluorine based resin.
 4. The polishing apparatus as set forth in claim 2, wherein the thickness of the resin coating is half or less of a projecting amount of the abrasive particles.
 5. The polishing apparatus as set forth in claim 1, wherein the chipping preventing portion for the abrasive particles comprises a ceramic coating covering the abrasive particles fixed to the first region.
 6. The polishing apparatus as set forth in claim 5, wherein the ceramic coating is formed of amorphous silicon carbide.
 7. The polishing apparatus as set forth in claim 5, wherein the thickness of the ceramic coating is half or less of a projecting amount of the abrasive particles.
 8. The polishing apparatus as set forth in claim 1, wherein the chipping preventing portion for the abrasive particles is provided in the first region where the abrasive particles are not fixed, and comprises a guide member composed of a resin material or a ceramic material.
 9. The polishing apparatus as set forth in claim 8, wherein the guide member is composed of a fluorine based resin, silicon nitride or silicon carbide.
 10. The polishing apparatus as set forth in claim 8, wherein a top of the guide member is located at a position lower by 20 μm or more than the highest position of a projecting height of the abrasive particles.
 11. The polishing apparatus as set forth in claim 1, wherein a width of the first region from an outer edge of the pellet-shaped grindstone is not less than 1% nor more than 10% of an outer diameter of the pellet-shaped grindstone.
 12. The polishing apparatus as set forth in claim 1, wherein an outer diameter of the pellet-shaped grindstone is 10 to 30 mm, and a width of the first region from an outer edge of the pellet-shaped grindstone is not less than 0.1 mm nor more than 3 mm.
 13. The polishing apparatus as set forth in claim 1, wherein the dresser comprises a plurality of pellet-shaped grindstones spaced from each other.
 14. The polishing apparatus as set forth in claim 1, wherein the abrasive particles comprise diamond abrasive particles and/or CBN abrasive particles.
 15. The polishing apparatus as set forth in claim 1, wherein the abrasive particles comprise irregular-type diamond abrasive particles.
 16. The polishing apparatus as set forth in claim 1, wherein the abrasive particles are fixed to a surface of a pellet-shaped member by electrodeposition, metal bonding, resin bonding, or brazing.
 17. The polishing apparatus as set forth in claim 1, wherein the polishing apparatus is a CMP apparatus.
 18. A method of manufacturing a semiconductor device using a polishing apparatus, the polishing apparatus comprising: a wafer polishing unit comprising a polishing surface plate, an abrasive supply part supplying an abrasive to a polishing pad placed on the polishing surface plate, and a wafer holding part holding a semiconductor wafer, the wafer polishing unit polishing a surface to be polished of the semiconductor wafer held on the wafer holding part by pressing the surface to be polished of the semiconductor wafer against the polishing pad; and a dressing unit comprising a dresser having a pellet-shaped grindstone with abrasive particles fixed to a surface thereof, the dressing unit dressing a surface of the polishing pad using the pellet-shaped grindstone, wherein the pellet-shaped grindstone has a first region along an outer peripheral portion thereof and a second region located inside the first region, and comprises a chipping preventing portion for the abrasive particles provided in the first region, the method comprising: polishing the surface to be polished of the semiconductor wafer held on the wafer holding part by pressing the surface to be polished of the semiconductor wafer against the polishing pad; and dressing the surface of the polishing pad using the pellet-shaped grindstone before, after, or during the polishing of the semiconductor wafer.
 19. The method of manufacturing a semiconductor device as set forth in claim 18, wherein the dressing includes relatively moving the dresser and the polishing pad while pressing an abrasive particles surface of the pellet-shaped grindstone against the surface of the polishing pad.
 20. The method of manufacturing a semiconductor device as set forth in claim 18, wherein the polishing is performed by a CMP method. 